2.1. Angiogenesis
Angiogenesis, defined as the growth or sprouting of new blood vessels from existing vessels, is a complex process that primarily occurs during embryonic development. Under normal physiological conditions in adults, angiogenesis takes place only in very restricted situations such as hair growth and wounding healing (Auerbach, W. and Auerbach, R., 1994, Pharmacol Ther 63(3):265–311; Ribatti et al., 1991, Haematologica 76(4):311–20; Risau, 1997, Nature 386(6626):671–4). Unregulated angiogenesis has gradually been recognized to be responsible for a wide range of disorders, including, but not limited to cardiovascular disease, cancer, rheumatoid arthritis, psoriasis and diabetic retinopathy (Folkman, 1995, Nat Med 1(1):27–31; Isner, 1999, Circulation 99(13): 1653–5; Koch, 1998, Arthritis Rheum 41(6):951–62; Walsh, 1999, Rheumatology (Oxford) 38(2): 103–12; Ware and Simons, 1997, Nat Med 3(2): 158–64).
2.2. Cardiac Disorders and Factors
Heart failure affects approximately five million Americans, and new cases of heart failure number about 400,000 each year. It is the single most frequent cause of hospitalization for people age 65 and older in the United States. Recent advances in the management of acute cardiac diseases, including acute myocardial infarction, are resulting in an expanding patient population that will eventually develop chronic heart failure. From 1979 to 1995, hospitalizations for congestive heart failure (CHF) rose from 377,000 to 872,000 (a 130 percent increase) and CHF deaths increased 116 percent.
CHF is a syndrome characterized by left ventricular dysfunction, reduced exercise tolerance, impaired quality of life, and markedly shortened life expectancy. The sine qua non of heart failure is an inability of the heart to pump blood at a rate sufficient to meet the metabolic needs of the body's tissues (in other words, there is insufficient cardiac output).
At least four major compensatory mechanisms are activated in the setting of heart failure to boost cardiac output, including peripheral vasoconstriction, increased heart rate, increased cardiac contractility, and increased plasma volume. These effects are mediated primarily by the sympathetic nervous system and the renin-angiotensin system. See, Eichhorn, American Journal of Medicine, 104: 163–169 (1998). Increased output from the sympathetic nervous system increases vascular tone, heart rate, and contractility. Angiotensin II elevates blood pressure by 1) directly stimulating vascular smooth muscle contraction, 2) promoting plasma volume expansion by stimulating aldosterone and antidiuretic hormone secretion, 3) stimulating sympathetic-mediated vascular tone, and 4) catalyzing the degradation of bradykinin, which has vasodilatory and natriuretic activity. See, review by Brown and Vaughan, Circulation, 97: 1411–1420 (1998). As noted below, angiotensin II may also have directly deleterious effects on the heart by promoting myocyte necrosis (impairing systolic function) and intracardiac fibrosis (impairing diastolic and in some cases systolic function). See, Weber, Circulation, 96: 4065–4082 (1998).
A consistent feature of congestive heart failure (CHF) is cardiac hypertrophy, an enlargement of the heart that is activated by both mechanical and hormonal stimuli and enables the heart to adapt to demands for increased cardiac output. Morgan and Baker, Circulation, 83: 13–25 (1991). This hypertrophic response is frequently associated with a variety of distinct pathological conditions such as hypertension, aortic stenosis, myocardial infarction, cardiomyopathy, valvular regurgitation, and intracardiac shunt, all of which result in chronic hemodynamic overload.
Hypertrophy is generally defined as an increase in size of an organ or structure independent of natural growth that does not involve tumor formation. Hypertrophy of the heart is due either to an increase in the mass of the individual cells (myocytes), or to an increase in the number of cells making up the tissue (hyperplasia), or both.
While the enlargement of an embryonic heart is largely dependent on an increase in myocyte number (which continues until shortly after birth), post-natal cardiac myocytes lose their proliferative capacity. Further growth occurs through hypertrophy of the individual cells.
Adult myocyte hypertrophy is initially beneficial as a short term response to impaired cardiac function by permitting a decrease in the load on individual muscle fibers. With severe, long-standing overload, however, the hypertrophied cells begin to deteriorate and die. Katz, “Heart Failure”, in: Katz A. M. ed., Physiology of the Heart (New York: Raven Press, 1992) pp.638–668. Cardiac hypertrophy is a significant risk factor for both mortality and morbidity in the clinical course of heart failure. Katz, Trends Cardiovasc. Med., 5: 37–44 (1995). For further details of the causes and pathology of cardiac hypertrophy see, e.g., Heart Disease, A Textbook of Cardiovascular Medicine, Braunwald, E. ed. (W.B. Saunders Co., 1988), Chapter 14, “Pathophysiology of Heart Failure.”
On a cellular level, the heart is composed of myocytes and surrounding support cells, generically called non-myocytes. While non-myocytes are primarily fibroblast/mesenchymal cells, they also include endothelial and smooth muscle cells. Indeed, although myocytes make up most of the adult myocardial mass, they represent only about 30% of the total cell numbers present in heart. In response to hormonal, physiological, hemodynamic, and pathological stimuli, adult ventricular muscle cells can adapt to increased workloads through the activation of a hypertrophic process. This response is characterized by an increase in myocyte cell size and contractile protein content of individual cardiac muscle cells, without concomitant cell division and activation of embryonic genes, including the gene for atrial natriuretic peptide (ANP). Chien et al., FASEB J., 5: 3037–3046 (1991); Chien et al., Annu. Rev. Physiol., 55: 77–95 (1993). An increment in myocardial mass as a result of an increase in myocyte size that is associated with an accumulation of interstitial collagen within the extracellular matrix and around intramyocardial coronary arteries has been described in left ventricular hypertrophy secondary to pressure overload in humans. Caspari et al., Cardiovasc. Res., 11: 554–558 (1977); Schwarz et al., Am. J. Cardiol., 42: 895–903 (1978); Hess et al., Circulation, 63: 360–371 (1981); Pearlman et al., Lab. Invest., 46: 158–164 (1982).
It has also been suggested that paracrine factors produced by non-myocyte supporting cells may additionally be involved in the development of cardiac hypertrophy, and various non-myocyte derived hypertrophic factors, such as, leukocyte inhibitory factor (LIF) and endothelin, have been identified. Metcalf, Growth Factors, 7: 169–173 (1992); Kurzrock et al., Endocrine Reviews, 12: 208–217 (1991); Inoue et al., Proc. Natl. Acad. Sci. USA, 86: 2863–2867 (1989); Yanagisawa and Masaki, Trends Pharm. Sci., 10: 374–378 (1989); U.S. Pat. No. 5,573,762 (issued Nov. 12, 1996). Further exemplary factors that have been identified as potential mediators of cardiac hypertrophy include cardiotrophin-1 (CT-1) (Pennica et al., Proc. Nat. Acad. Sci. USA, 92: 1142–1146 (1995)), catecholamines, adrenocorticosteroids, angiotensin, and prostaglamidins.
At present, the treatment of cardiac hypertrophy varies depending on the underlying cardiac disease.
Catecholamines, adrenocorticosteroids, angiotensin, prostaglamidins, LIF, endothelin (including endothelin-1, -2, and -3 and big endothelin), and CT-1 are among the factors identified as potential mediators of hypertrophy. For example, beta-adrenergic receptor blocking drugs (beta-blockers, e.g., propranolol, timolol, tertalolol, carteolol, nadolol, betaxolol, penbutolol, acetobutolol, atenolol, metoprolol, carvedilol, etc.) and verapamil have been used extensively in the treatment of hypertrophic cardiomyopathy. The beneficial effects of beta-blockers on symptoms (e.g., chest pain) and exercise tolerance are largely due to a decrease in the heart rate with a consequent prolongation of diastole and increased passive ventricular filling. Thompson et al., Br. Heart J., 44: 488–98 (1980); Harrison et al., Circulation, 29: 84–98 (1964). Verapamil has been described to improve ventricular filling and probably reducing myocardial ischemia. Bonow et al., Circulation, 72: 853–64 (1985).
Nifedipine and diltiazem have also been used occasionally in the treatment of hypertrophic cardiomyopathy. Lorell et al., Circulation, 65: 499–507 (1982); Betocchi et al., Am. J. Cardiol., 78: 451–457 (1996). However, because of its potent vasodilating properties, nifedipine may be harmful, especially in patients with outflow obstruction. Disopyramide has been used to relieve symptoms by virtue of its negative inotropic properties. Pollick, N. Engl. J. Med., 307: 997–999 (1982). In many patients, however, the initial benefits decrease with time. Wigle et al., Circulation, 92: 1680–1692 (1995). Antihypertensive drug therapy has been reported to have beneficial effects on cardiac hypertrophy associated with elevated blood pressure. Examples of drugs used in antihypertensive therapy, alone or in combination, are calcium antagonists, e.g., nitrendipine; adrenergic receptor blocking agents, e.g., those listed above; angiotensin converting enzyme (ACE) inhibitors such as quinapril, captopril, enalapril, ramipril, benazepril, fosinopril, and lisinopril; diuretics, e.g., chlorothiazide, hydrochlorothiazide, hydroflumethazide, methylchlothiazide, benzthiazide, dichlorphenamide, acetazolamide, and indapamide; and calcium channel blockers, e.g., diltiazem, nifedipine, verapamil, and nicardipine.
For example, treatment of hypertension with diltiazem and captopril showed a decrease in left ventricular muscle mass, but the Doppler indices of diastolic function did not normalize. Szlachcic et al., Am. J. Cardiol., 63: 198–201 (1989); Shahi et al., Lancet, 336: 458–461 (1990). These findings were interpreted to indicate that excessive amounts of interstitial collagen may remain after regression of left ventricular hypertrophy. Rossi et al., Am. Heart J., 124: 700–709 (1992). Rossi et al., supra, investigated the effect of captopril on the prevention and regression of myocardial cell hypertrophy and interstitial fibrosis in pressure overload cardiac hypertrophy, in experimental rats.
Agents that increase cardiac contractility directly (iontropic agents) were initially thought to benefit patients with heart failure because they improved cardiac output in the short term. However, all positive inotropic agents except digoxigenin have been found to result in increased long-term mortality, in spite of short-term improvements in cardiac performance. Massie, Curr. Op. in Cardiology, 12: 209–217 (1997); Reddy et al., Curr. Opin. Cardiol, 12: 233–241 (1997). Beta-adrenergic receptor blockers have recently been advocated for use in heart failure. Evidence from clinical trials suggests that improvements in cardiac function can be achieved without increased mortality, though documented improvements of patient survival have not yet been demonstrated. See also, U.S. Pat. Nos. 5,935,924, 5,624,806; 5,661,122; and 5,610,134 and WO 95/28173 regarding the use of cardiotropin-1 or antagonists thereof, or growth hormone and/or insulin-like growth factor-I in the treatment of CHF. Another treatment modality is heart transplantation, but this is limited by the availability of donor hearts.
Endothelin is a vasoconstricting peptide comprising 21 amino acids, isolated from swine arterial endothelial culture supernatant and structurally determined. Yanagisawa et al., Nature, 332: 411–415 (1988). Endothelin was later found to exhibit various actions, and endothelin antibodies as endothelin antagonists have proven effective in the treatment of myocardial infarction, renal failure, and other diseases. Since endothelin is present in live bodies and exhibits vasoconstricting action, it is expected to be an endogenous factor involved in the regulation of the circulatory system, and may be associated with hypertension, cardiovascular diseases such as myocardial infarction, and renal diseases such as acute renal failure. Endothelin antagonists are described, for example, in U.S. Pat. No. 5,773,414; JP Pat. Publ. 3130299/1991, EP 457,195; EP 460,679; and EP 552,489. A new endothelin B receptor for identifying endothelin receptor antagonists is described in U.S. Pat. No. 5,773,223.
Current therapy for heart failure is primarily directed to using angiotensin-converting enzyme (ACE) inhibitors, such as captopril, and diuretics. These drugs improve hemodynamic profile and exercise tolerance and reduce the incidence of morbidity and mortality in patients with CHF. Kramer et al., Circulation, 67(4): 807–816 (1983); Captopril Multicenter Research Group, J.A.C.C., 2(4): 755–763 (1983); The CONSENSUS Trial Study Group, N. Engl. J. Med., 316(23): 1429–1435 (1987); The SOLVD Investigators, N. Engl. J. Med., 325(5):293–302 (1991). Further, they are useful in treating hypertension, left ventricular dysfunction, atherosclerotic vascular disease, and diabetic nephropathy. Brown and Vaughan, supra. However, despite proven efficacy, response to ACE inhibitors has been limited. For example, while prolonging survival in the setting of heart failure, ACE inhibitors appear to slow the progression towards end-stage heart failure, and substantial numbers of patients on ACE inhibitors have functional class III heart failure.
Moreover, improvement of functional capacity and exercise time is only small and mortality, although reduced, continues to be high. The CONSENSUS Trial Study Group, N. Engl. J. Med., 316(23): 1429–1453(1987); The SOLVD Investigators, N. Engl. J. Med., 325(5):293–302(1991); Cohn et al., N. Engl. J. Med., 325(5):303–310 (1991); The Captopril-Digoxin Multicenter Research Group, JAMA, 259(4): 539–544 (1988). Hence, ACE inhibitors consistently appear unable to relieve symptoms in more than 60% of heart failure patients and reduce mortality of heart failure only by approximately 15–20%. For further adverse effects, see Brown and Vaughan, supra.
An alternative to ACE inhibitors is represented by specific AT1 receptor antagonists. Clinical studies are planned to compare the efficacy of these two modalities in the treatment of cardiovascular and renal disease. However, animal model data suggests that the ACE/Ang II pathway, while clearly involved in cardiac hypertrophy, is not the only, or even the primary pathway active in this role. Mouse genetic “knockout” models have been made to test individual components of the pathway. In one such model, the primary cardiac receptor for Ang II, AT sub 1A, has been genetically deleted; these mice do not develop hypertrophy when Ang II is given experimentally (confirming the basic success of the model in eliminating hypertrophy secondary to Ang II). However, when the aorta is constricted in these animals (a model of hypertensive cardiac stress), the hearts still become hypertrophic. This suggests that alternative signaling pathways, not depending on this receptor (AT sub 1A), are activated in hypertension. ACE inhibitors would presumably not be able to inhibit these pathways. See, Harada et al., Circulation, 97: 1952–1959 (1998). See also, Homcy, Circulation, 97: 1890–1892 (1998) regarding the enigma associated with the process and mechanism of cardiac hypertrophy.
About 750,000 patients suffer from acute myocardial infarction (AMI) annually, and approximately one-fourth of all deaths in the United States are due to AMI. In recent years, thrombolytic agents, e.g., streptokinase, urokinase, and in particular tissue plasminogen activator (t-PA) have significantly increased the survival of patients who suffered myocardial infarction. When administered as a continuous intravenous infusion over 1.5 to 4 hours, t-PA produces coronary patency at 90 minutes in 69% to 90% of the treated patients. Topol et al., Am. J. Cardiol., 61: 723–728 (1988); Neuhaus et al., J. Am. Coll. Cardiol., 12: 581–587 (1988); Neuhaus et al., J. Am. Coll. Cardiol., 14: 1566–1569 (1989). The highest patency rates have been reported with high dose or accelerated dosing regimens. Topol, J. Am. Coll. Cardiol., 15: 922–924 (1990). t-PA may also be administered as a single bolus, although due to its relatively short half-life, it is better suited for infusion therapy. Tebbe et al., Am. J. Cardiol., 64: 448–453 (1989). A t-PA variant, specifically designed to have longer half-life and very high fibrin specificity, TNK t-PA (a T103N, N117Q, KHRR(296–299)AAAA t-PA variant, Keyt et al., Proc. Natl. Acad. Sci. USA, 91: 3670–3674 (1994)) is particularly suitable for bolus administration. However, despite all these advances, the long-term prognosis of patient survival depends greatly on the post-infarction monitoring and treatment of the patients, which should include monitoring and treatment of cardiac hypertrophy.
2.3. Growth Factors
Various naturally occurring polypeptides reportedly induce the proliferation of endothelial cells. Among those polypeptides are the basic and acidic fibroblast growth factors (FGF) (Burgess and Maciag, Annual Rev. Biochem., 58: 575 (1989)), platelet-derived endothelial cell growth factor(PD-ECGF) (Ishikawa et al., Nature, 338: 557 (1989)), and vascular endothelial growth factor (VEGF). Leung et al., Science, 246: 1306 (1989); Ferrara and Henzel, Biochem. Biophys. Res. Commun., 161: 851 (1989); Tischer et al., Biochem. Biophys. Res. Commun., 165: 1198 (1989); EP 471,754B granted Jul. 31, 1996.
Media conditioned by cells transfected with the human VEGF (hVEGF) cDNA promoted the proliferation of capillary endothelial cells, whereas control cells did not. Leung et al., Science, 246: 1306 (1989). Several additional cDNAs were identified in human cDNA libraries that encode 121-, 189-, and 206-amino acid isoforms of hVEGF (also collectively referred to as hVEGF-related proteins). The 121-amino acid protein differs from hVEGF by virtue of the deletion of the 44 amino acids between residues 116 and 159 in hVEGF. The 189-amino acid protein differs from hVEGF by virtue of the insertion of 24 amino acids at residue 116 in hVEGF, and apparently is identical to human vascular permeability factor (hVPF). The 206-amino acid protein differs from hVEGF by virtue of an insertion of 41 amino acids at residue 116 in hVEGF. Houck et al., Mol. Endocrin., 5: 1806 (1991); Ferrara et al., J. Cell. Biochem., 47: 211 (1991); Ferrara et al., Endocrine Reviews, 13: 18 (1992); Keck et al., Science, 246: 1309 (1989); Connolly et al., J. Biol. Chem., 264: 20017 (1989); EP 370,989 published May 30, 1990.
It is now well established that angiogenesis, which involves the formation of new blood vessels from preexisting endothelium, is implicated in the pathogenesis of a variety of disorders. These include solid tumors and metastasis, atherosclerosis, retrolental fibroplasia, hemangiomas, chronic inflammation, intraocular neovascular syndromes such as proliferative retinopathies, e.g., diabetic retinopathy, age-related macular degeneration (AMD), neovascular glaucoma, immune rejection of transplanted corneal tissue and other tissues, rheumatoid arthritis, and psoriasis. Folkman et al., J. Biol. Chem., 267: 10931–10934 (1992); Klagsbrun et al., Annu. Rev. Physiol., 53: 217–239 (1991); and Garner A., “Vascular diseases”, In: Pathobiology of Ocular Disease. A Dynamic Approach, Garner A., Klintworth G K, eds., 2nd Edition (Marcel Dekker, NY, 1994), pp 1625–1710.
In the case of tumor growth, angiogenesis appears to be crucial for the transition from hyperplasia to neoplasia, and for providing nourishment for the growth and metastasis of the tumor. Folkman et al., Nature, 339: 58(1989). The neovascularization allows the tumor cells to acquire a growth advantage and proliferative autonomy compared to the normal cells. A tumor usually begins as a single aberrant cell which can proliferate only to a size of a few cubic millimeters due to the distance from available capillary beds, and it can stay ‘dormant’ without further growth and dissemination for a long period of time. Some tumor cells then switch to the angiogenic phenotype to activate endothelial cells, which proliferate and mature into new capillary blood vessels. These newly formed blood vessels not only allow for continued growth of the primary tumor, but also for the dissemination and recolonization of metastatic tumor cells. Accordingly, a correlation has been observed between density of microvessels in tumor sections and patient survival in breast cancer as well as in several other tumors. Weidner et al., N. Engl. J. Med, 324: 1–6 (1991); Horak et al., Lancet, 340: 1120–1124 (1992); Macchiarini et al., Lancet, 340: 145–146 (1992). The precise mechanisms that control the angiogenic switch is not well understood, but it is believed that neovascularization of tumor mass results from the net balance of a multitude of angiogenesis stimulators and inhibitors (Folkman, 1995, Nat Med 1(1):27–31).
The search for positive regulators of angiogenesis has yielded many candidates, including aFGF, bFGF, TGF-α, TGF-β, HGF, TNF-α, angiogenin, IL-8, etc. Folkman et al., J.B.C., supra, and Klagsbrun et al., supra. The negative regulators so far identified include thrombospondin (Good et al., Proc. Natl. Acad. Sci. USA., 87: 6624–6628 (1990)), the 16-kilodalton N-terminal fragment of prolactin (Clapp et al., Endocrinology, 133: 1292–1299 (1993)), angiostatin (O'Reilly et al., Cell, 79: 315–328 (1994)), and endostatin. O'Reilly et al., Cell, 88: 277–285 (1996).
Work done over the last several years has established the key role of VEGF, not only in stimulating vascular endothelial cell proliferation, but also in inducing vascular permeability and angiogenesis. Ferrara et al., Endocr. Rev., 18: 4–25 (1997). The finding that the loss of even a single VEGF allele results in embryonic lethality points to an irreplaceable role played by this factor in the development and differentiation of the vascular system. Furthermore, VEGF has been shown to be a key mediator of neovascularization associated with tumors and intraocular disorders. Ferrara et al., Endocr. Rev., supra. The VEGF mRNA is overexpressed by the majority of human tumors examined. Berkman et al., J. Clin. Invest., 91: 153–159 (1993); Brown et al., Human Pathol., 26: 86–91 (1995); Brown et al., Cancer Res., 53: 4727–4735 (1993); Mattern et al., Brit. J. Cancer, 73: 931–934 (1996); Dvorak et al., Am. J. Pathol., 146: 1029–1039 (1995).
Also, the concentration levels of VEGF in eye fluids are highly correlated to the presence of active proliferation of blood vessels in patients with diabetic and other ischemia-related retinopathies. Aiello et al., N. Engl. J. Med., 331: 1480–1487 (1994). Furthermore, recent studies have demonstrated the localization of VEGF in choroidal neovascular membranes in patients affected by AMD. Lopez et al., Invest. Ophthalmol. Vis. Sci., 37: 855–868 (1996).
Anti-VEGF neutralizing antibodies suppress the growth of a variety of human tumor cell lines in nude mice (Kim et al., Nature, 362: 841–844 (1993); Warren et al., J. Clin. Invest., 95: 1789–1797 (1995); Borgström et al., Cancer Res., 56: 4032–4039 (1996); Melnyk et al., Cancer Res., 56: 921–924 (1996)) and also inhibit intraocular angiogenesis in models of ischemic retinal disorders. Adamis et al., Arch. Ophthalmol., 114: 66–71 (1996). Therefore, anti-VEGF monoclonal antibodies or other inhibitors of VEGF action are promising candidates for the treatment of solid tumors and various intraocular neovascular disorders. Such antibodies are described, for example, in EP 817,648 published Jan. 14, 1998 and in WO98/45331 and WO98/45332 both published Oct. 15, 1998.
There exist several other growth factors and mitogens, including transforming oncogenes, that are capable of rapidly inducing a complex set of genes to be expressed by certain cells. Lau and Nathans, Molecular Aspects of Cellular Regulation, 6: 165–202 (1991). These genes, which have been named immediate-early- or early-response genes, are transcriptionally activated within minutes after contact with a growth factor or mitogen, independent of de novo protein synthesis. A group of these intermediate-early genes encodes secreted, extracellular proteins that are needed for coordination of complex biological processes such as differentiation and proliferation, regeneration, and wound healing. Ryseck et al., Cell Growth Differ., 2: 235–233 (1991).
Highly-related proteins that belong to this group include cef 10 (Simmons et al., Proc. Natl. Acad. Sci. USA, 86: 1178–1182 (1989)), cyr 61, which is rapidly activated by serum- or platelet-derived growth factor (PDGF) (O'Brien et al., Mol. Cell Biol., 10: 3569–3577 (1990), human connective tissue growth factor (CTGF) (Bradham et al., J. Cell. Biol., 114: 1285–1294 (1991)), which is secreted by human vascular endothelial cells in high levels after activation with transforming growth factor beta (TGF-β), exhibits PDGF-like biological and immunological activities, and competes with PDGF for a particular cell surface receptor, fisp-12 (Ryseck et al., Cell Growth Differ., 2: 235–233 (1991)), human vascular IBP-like growth factor (VIGF) (WO 96/17931), and nov, normally arrested in adult kidney cells, which was found to be overexpressed in myeloblastosis-associated-virus-type-1-induced nephroblastomas. Joloit et al., Mol. Cell. Biol., 12: 10–21 (1992).
The expression of these immediate-early genes acts as “third messengers” in the cascade of events triggered by growth factors. It is also thought that they are needed to integrate and coordinate complex biological processes, such as differentiation and wound healing in which cell proliferation is a common event.
As additional mitogens, insulin-like growth factor binding proteins (IGFBPs) have been shown, in complex with insulin-like growth factor (IGF), to stimulate increased binding of IGF to fibroblast and smooth muscle cell surface receptors. Clemmons et al., J. Clin. Invest., 77: 1548 (1986). Inhibitory effects of IGFBP on various IGF actions in vitro include stimulation of glucose transport by adipocytes, sulfate incorporation by chondrocytes, and thymidine incorporation in fibroblast. Zapf et al., J. Clin. Invest, 63: 1077 (1979). In addition, inhibitory effects of IGFBPs on growth factor-mediated mitogen activity in normal cells have been shown.
2.4. Need for Further Treatments
In view of the role of vascular endothelial cell growth and angiogenesis in many diseases and disorders, it is desirable to have a means of reducing or inhibiting one or more of the biological effects causing these processes. It is also desirable to have a means of assaying for the presence of pathogenic polypeptides in normal and diseased conditions, and especially cancer. Further, in a specific aspect, as there is no generally applicable therapy for the treatment of cardiac hypertrophy, the identification of factors that can prevent or reduce cardiac myocyte hypertrophy is of primary importance in the development of new therapeutic strategies to inhibit pathophysiological cardiac growth. While there are several treatment modalities for various cardiovascular and oncologic disorders, there is still a need for additional therapeutic approaches.